1. Field of the Invention
The present invention relates to a metal semiconductor optical device and, more particularly, to a metal semiconductor optical device which is capable of effectively enhancing an absorption rate and hence characteristics of interface of a junction, through the use of Schottky barrier effect presenting in the junction between a metal thin film and a semiconductor substrate.
2. Description of the Prior Art
In general, in metal semiconductor optical devices, it should be formed on a metal contact surface an extremely thin film metal so as to overcome degradation of optical efficiency inducing by reflection and absorption of light beam from and to the surface, when the light beam is illuminated onto the metal contact surface. In case of a photodiode or a solar battery using Schottky barrier effect presented in junction surface in the metal oxide semiconductor, there are three types of photo current components: one is light with hv&gt;Vs(the Schottky barrier) which is absorbed on a metal layer and exceed to the Schottky barrier and excites electrons within the semiconductor; another is that with hv&gt;Eg of a shortwave length which is mainly entered to a depletion region and delivered to the semiconductor, and the other that with hv=Eg which is entered to a neutral region. The solar battery using such Schottky barrier effect should be manufactured an extremely thin metal so as to absorb a considerable amount of light beam.
Referring to FIG. 1, there is shown a cross-sectional view of a solar battery using the Schottky barrier which is the metal semiconductor optical device previously disclosed. As presented in FIG. 1, the solar battery has a structure that a metal thin film 2 is formed on a portion of semiconductor substrate 1, a dielectric film 3 is deposited on the other portion of the semiconductor substrate 1, i.e., at sides of the metal thin film 1, an anti-reflection film 4 is provided on the metal thin film 2 to prevent light beam impinged onto the metal thin film 2 from reflecting therefrom, electrodes 5, 5 are cantilevered from edge portion of the metal thin film 2, and a rear electrode 6 is formed on bottom surface of the semiconductor substrate 1.
The solar battery with the above identified structure has advantages that its fabricating step can be performed at lower temperature, and it may easily be adapted to a polycrystal and a thin film solar battery, and hence, it generates a higher output power (for this reason, it exist the depletion region within the semiconductor).
As stated above, in case of the photodiode or the solar battery utilizing the metal semiconductor junction, in order to increase an optical absorption factor and the transition efficiency of light energy to electric energy, the metal thin film should be extremely thinly formed, for example, in a thickness of approximately 100.ANG.. Unfortunately, in the prior art photodiode or solar battery, since the metal film is directly deposited on the semiconductor substrate 1 to obtain the metal semiconductor junction structure, the metal thin film may not be uniformly formed on the substrate 1.
Accordingly, a thickness of the metal film to be deposited thereon sufficiently should be thick so as to evenly deposit on the substrate. Furthermore, due to the influence of an interface electric band entailed at junction the metal thin film and the semiconductor, it suffers from shortcomings that the optical absorption factor of light beam on the metal film is degraded and hence the transition efficiency of light to electric energies is decreased.